In the production of silicon compositions, transition metal catalysts have long been known to promote the hydrosilation reaction. In addition to catalyzing the hydrosilation reaction, many transition metals, in the presence of silicon hydrides (Sixe2x80x94H), also promote epoxide ring-opening polymerization of the ethylenically unsaturated epoxide starting material and the epoxysilane or epoxysilicone product of the hydrosilation reaction. This epoxide ring-opening polymerization reaction during production of an epoxysilane or epoxysilicone can lead to gelation, and may result in both the loss of the entire batch and in considerable loss of time to remove the insoluble gelled resin. Additionally, a partial gelation can occur during epoxysilicone synthesis such that reproducible batch-to-batch viscosities of the epoxysilicone product may be difficult to obtain.
In the presence of precious metal hydrosilation catalysts, e.g., chloroplatinic acid, epoxysilicones have been found to gel slowly on storage at room temperature due to the epoxide ring-opening polymerization, thus shortening the shelf life of the epoxysilicone product. This storage problem can be partially alleviated by adding a hydrochloride acceptor to the reaction to sequester HCl present from decomposition of the catalyst, as reported in U.S. Pat. No. 4,083,856 (F. Mendicino).
The prior art has taught that the epoxide ring-opening polymerization side reaction does not occur in the rhodium-catalyzed hydrosilation reaction of an ethylenically unsaturated epoxide and a Sixe2x80x94H. For example, U.S. Pat. No. 5,442,026 (Crivello et al.), U.S. Pat. No. 5,169,962 (Crivello et al.), U.S. Pat. No. 4,804,768 (Quirk et al.) teach that rhodium catalysts such as Wilkinson""s catalyst, RhCl3 hydrate, RhH(CO)(PPh3)3 can be used to produce epoxysilicones. In addition to rhodium catalysts, certain platinum catalyst systems have been reported to selectively catalyze the hydrosilation reaction of ethylenically unsaturated epoxides and a Sixe2x80x94H versus the epoxide ring-opening polymerization side reaction, as disclosed in U.S. Pat. No. 5,583,194 (Crivello et al.) which teaches that quaternary onium hexachloroplatinate salts, e.g., (R4M)2PtCl6, or as disclosed U.S. Pat. No. 5,260,399 (Crivello et al.) transition metal phosphine complexes, e.g., Pt(PPh3)4, can be used to produce epoxysilicon compositions. However, these catalysts have not achieved commercial acceptance yet.
U.S. Pat. Nos. 5,240,971, 5,227,420, and 5,258,480 (Eckberg et al.) reported the preparation of epoxysilicones using either RhCl3[S(n-Bu)2]3 or PtCl2(SEt2)2 as the catalyst in the presence of a tertiary amine to control the viscosity during the hydrosilation reaction. However, only a limited number of transition metal catalysts are active in the presence of this stabilizer.
Carboxylic acids have been reported to promote the transition metal catalyzed hydrosilation reaction, as disclosed in JP 11 180,986 (M. Tachhikawa; K. Takei), F. Mendicino; C. Schilling Jr. Abstract of Papers, 32nd Organosilicon Symposium; 1999; P-68, and in UDC 415,268 (Belyakova et al.). But, carboxylic acid salts have not. Carboxylic acid salts have been reported to prevent acetal formation through the hydroxyl groups of a silicone polyether copolymer as disclosed in U.S. Pat. No. 4,847,398 (K. R. Mehta et al.); however, no utility for epoxides is disclosed.
The literature does mention that alcohols prevent or retard the epoxide ring-opening polymerization reaction (A. K. McMullen; et al. Abstract of Papers, 27th Organosilicon Symposium, 1994; Abstract P-45; and Crivello et al. Polym. Preps. 1991, 32, 338).
It is apparent that there exists a need in the industry for a method to eliminate epoxide ring-opening polymerization, and olefin isomerization when commonly used hydrosilation catalysts, such chloroplatinic acid, are employed. There is also a need for an efficient yet economical method of producing epoxysilicone monomers and oligomers in the absence of the epoxide ring-opening polymerization reaction, thereby generating epoxysilicon compositions of reproducible batch-to-batch viscosity. There is additionally a need for epoxysilicon compositions that are stable to the epoxide ring-opening polymerization reaction and therefore have increased the shelf life without an additional processing step.
The object of this invention is to provide a method for preparing epoxy organosilicon compositions through the platinum metal-catalyzed hydrosilation reaction between an ethylenically unsaturated epoxide and a hydrido organosilicon in the presence of a carboxylic acid salt where the catalyst efficiently promotes the hydrosilation reaction without also promoting either the epoxide ring-opening polymerization reaction of either the ethylenically unsaturated epoxide starting material, the epoxysilicon composition or the isomerization of the ethylenically unsaturated epoxide starting material. Compositions of epoxy organosilicon compounds and the salt of the carboxylic acid are taught as well wherein the salt suppresses the reactivity of the epoxy functionality.
According to the process of the invention, the platinum-catalyzed hydrosilation of an ethylenically unsaturated epoxide with either a hydrido silane or hydrido siloxane occurs in the presence of a carboxylic acid salt without epoxide ring-opening polymerization side reaction, allowing for the production of high yields of epoxyorgano silanes or siloxanes. For certain carboxylic acid salts, both epoxide ring-opening polymerization and olefin isomerization are suppressed. This inventive process allows for greater batch-to-batch consistencies without the use of more complex catalyst systems. While the process is useful for both siloxanes and silanes, given that the internal rearrangement of the olefin is more of an issue in the hydrosilation of a silane, the present invention will find greater utility in the hydrosilation of hydrido alkoxysilanes.
These salts are also useful for the suppression of the reactivity of the epoxide after the hydrosilation reaction and thus are useful to extend the shelf life of epoxy organosilicon materials, even if post added after hydrosilation.
Ethylenically unsaturated epoxides for use herein include linear or cycloaliphatic epoxy compounds wherein the unsaturation is terminal (i.e., xc2x1, 2) which contain from 4 to 50 carbon atoms. The epoxide may be visualized as an ethylenically unsaturated epoxide of the formula: 
where R can be a single bond or an alkylene optionally containing alkyl pendant groups; R1, R2 and R3 can individually be hydrogen, alkyl straight, branched or cyclic, or any two of R1, R2 or R3 can be alkylene and combined to form a 5 to 12 carbon cyclic ring, optionally containing alkyl pendants; and the number of carbon atoms in R, R1, R2, and R3 are such that the total number of carbon atoms in the epoxide is from 4 to 50. Some representative epoxides are: 4vinylcyclohexene monoxide, 1-methyl-4-isopropenyl cyclohexene monoxide, and butadiene monoxide. The preferred epoxide is 4-vinylcyclohexene monoxide.
The hydridosilanes may be alkoxy silanes. The hydrido alkoxysilanes that may be used include the trialkoxysilanes, such as trimethoxysilane, triethoxysilane, tri-n-propoxysilane, and triisopropoxysilane. Trimethoxysilane and triethoxysilane are preferred. Other hydroalkoxysilanes include dialkoxysilanes such as methyldimethoxysilane, methyldiethoxysilane, dimethylmethoxysilane, and dimethylethoxysilane. Hydrosilanes in general can be represented by the formula R4n(OR4)3xe2x88x92nSiH, wherein R4 is a branched or linear alkyl group of 1 to 18 carbon atoms, a cyclic alkyl group of four to eight carbon atoms or an aryl, alkaryl, an aralkyl group of six to twelve carbon atoms, optionally containing halogen, oxygen, or nitrogen substituents with the proviso that such substituents do not interfere with either hydrosilation or promotion, and n is an integer selected from 0, 1, and 2. R4 is preferably a C1-C2 alkyl wherein n is preferably 1 or 0.
The hydrido organosiloxanes have the general formula:
[R5a(H)bSiO(4xe2x88x92axe2x88x92b)/2]n
wherein R5 represents a monovalent hydrocarbon radical, a has a value of from 1 to 2.99, b has a value of from 0.001 to 1, and the sum of a+b has a value of from 1.5 to 3.0 and n=2 to 400. More specifically, examples of the silicone hydride are heptamethyltrisiloxane (MDxe2x80x2M), tetramethyldisiloxane (Mxe2x80x2Mxe2x80x2), cyclic siloxanes DjDxe2x80x2k, and linear siloxanes MDxDxe2x80x2yM, wherein M=xe2x80x94Oxc2xdSi(CH3)3, Mxe2x80x2=xe2x80x94Oxc2xdSi(H)(CH3)2, Dxe2x80x2=xe2x80x94OSi(H)(CH3)xe2x80x94, D=xe2x80x94OSi(CH3)2xe2x80x94, j=1 to 8, kxe2x89xa71 and j+k=4 to 8, x=0 to 200 and y=1 to 200. Preferably j+k=4 to 5, x=1 to 20 and y=1 to 50.
The salt of the carboxylic acid may be represented by the formula R6CO2M wherein M represents an alkali, alkaline earth, transition metal, or an ammonium ion and R6 represents a monovalent hydrocarbon of one to 18 carbon atoms, which may be substituted with amino groups, hydroxyl functionalities, carboxyl groups or ester groups. Preferably R6 is a linear or branched alkyl of one to ten carbons or an aryl or alkaryl of 6 to 12 carbons. Specific examples of carboxylic acid salts include one or more salts of the alkali metals, e.g., lithium acetate, sodium acetate, potassium acetate, potassium benzoate, sodium trifluoroacetate or sodium propionate, of the alkaline earth metals, e.g., calcium acetate, of the transition metals, e.g., samarium (III) acetate, copper (II) acetate, copper (II) ethylhexanoate, indium (III) acetate, and nonquaternary ammonium or phosphonium, e.g., ammonium formate, ammonium acetate, ammonium isovalerate, ammonium 2ethylbutyrate, ammonium propionate or combinations of salts such as ammonium chloride and sodium acetate are suitable with this process, with ammonium salts of carboxylic acids being preferred, and ammonium propionate being the most preferred carboxylate salt. The acid may be a hydroxy acid, but only when the organosilicon hydride is an organosiloxane. The acid may be an amino acid, e.g., lysine or glutamic acid, but said acids are not preferred since they do not reduce olefin isomerization. Polymeric acids, such as polyacrylic acid may be used, in which case some of the acid may be left in acid form, i.e., it does not have to be neutralized to the salt form.
In the method of this invention, the present carboxylic acid salts are most useful in the range of 1 to about 10000 parts per million (ppm), preferably in the range of 200 to about 5000 ppm, and most preferably in the range of 100 to about 500 ppm based upon the weight of the ethylenically unsaturated epoxide.
The platinum catalyst can be of any form of platinum, which catalyzes the hydrosilation reaction of an ethylenically unsaturated epoxide and a silicon hydride. Platinum catalysts useful in the process of the invention include: hexachloroplatinic acid, various solutions derived from chloroplatinic acid, tris(tetramethyldivinyldisiloxane)diplatinum (0), phosphine complexes of platinum, and bis(acetylacetonate)platinum (II). The preferred catalyst in the practice of this invention is derived from a solution of hexachloroplatinic acid, where the most preferable catalyst is derived from a 10% (wt/wt) solution of hexachloroplatinic acid in ethanol. In the method of this invention, said catalysts are most useful in the range of 1 to about 5000 parts per million (ppm), preferably in the range of 1-500 ppm, and most preferred in the range of 5-50 ppm of platinum, based upon the weight of the combined weight of both the ethylenically unsaturated epoxide and SiH containing reactant.
This reaction can be carried out over a wide range of temperatures and pressures; however, the usual temperature range is from 50xc2x0 C. to about 175xc2x0 C. with the preferred temperature range being from about 75xc2x0 C. to 125xc2x0 C. The preferred pressure is atmospheric pressure. The duration of the reaction will be dependent on catalyst concentration and the reaction temperature. At higher catalyst concentrations and temperatures, the reaction will require less reaction time. The residence time within the reactor is not critical but should be sufficient to achieve a satisfactory degree of conversion to the hydrosilated product, i.e.,  greater than 80%, within acceptable limits given the volume of the equipment and the desired rate of production. Typical acceptable residence times are on the order of 0.5 to 4 hours. The reaction is usually conducted with no solvent, although a solvent may be used. Any hydrocarbon may be used such as octane, toluene or xylene.
This reaction can be conducted in the presence of excess olefin or silicon hydride, where the preferred reaction conditions are with a molar excess of olefin. The usual substrate concentration for conducting the reaction is either a 1.5:1.0 to a 1.0:1.5 molar ratio of olefin to silicon hydride (based on moles of hydrogen), preferably a ratio of 1.0:1.0 to 1.5:1.0 and preferred conditions are a 1.01:1.0 to 1.20:1.0 molar ratio of olefin to silicon hydride. The preferred catalyst system can be generated by mixing the catalyst and carboxylic acid salt in the olefin or the carboxylic acid salt can be added to the silicon composition after the hydrosilation reaction is complete. A catalyst promoter such as a carboxylic acid or an alcohol may be used with the carboyxlic acid salt, if necessary.
The resulting product may be purified for use, e.g., by stripping or distillation, as required.
The hydrosilation may be conducted batchwise, semi-batchwise or continuously as is known in the art.